Screaming CowbirdMolothrus rufoaxillaris

The Screaming Cowbird is a specialist brood parasite, parasitizing almost exclusively the Bay-winged Cowbird (Agelaioides badius). This host-parasitic relationship was first realized on 12 April 1873 by W. H. Hudson (1874, 1920) when he collected, from a flock of Bay-winged Cowbirds, young Screaming Cowbirds, which were molting from their "Bay-winged" juvenile plumage to the "Screaming Cowbird" adult plumage. Hudson then understood that the "extra" eggs in Bay-winged Cowbird nests must be those of the Screaming Cowbird -- "the eggs of the two species are identical in form, size, and coloration, and that, stranger still, the mimicry is as perfect in the young birds as in the eggs" (Hudson 1874: 162; see also Hudson 1920: 104). Because of this in-the-nest similarity, information of both species are presented for comparative purposes in some sections of this account.